As the demand for improved semiconductor device performance continues to increase, so too does the need for improved semiconductor device characterization techniques. Semiconductor wafers, such as silicon wafers, play an important role in the fabrication of device structures. Such device structures include, but are not limited to, semiconductor structures and related features associated with light emitting diodes (e.g., MOCVD grown structures). Improved monitoring of LED quality and fabrication control is critical in the development of advanced semiconductor device fabrication techniques. Internal quantum efficiency (IQE) is a common indicator for LED performance and is important for FOEL process control for the purposes of improving yield and quality of LED devices.
One characterization technique previously used to monitor electroluminescence and IQE includes a spring loaded probe contact technique. Spring loaded contact measurement techniques are described generally in U.S. Pat. No. 7,679,381, issued on Mar. 16, 2010; U.S. Patent Publication No. 2013/0043875, filed on Dec. 21, 2011; and U.S. Patent Publication No. 2013/0046496, filed on Dec. 21, 2011, which are each incorporated herein by reference in the entirety. The spring loaded contact technique is based on the measurement of electroluminescence intensity stimulated by a forward voltage, which is applied to a spring loaded probe, with reference to a bottom n-layer. The connection to the bottom n-layer is established through edge of the wafer with a second probe.
This technique also suffers from a number of disadvantages. One of the primary disadvantages of this technique is that the electroluminescence proximate to the contact area of the probe is obstructed by the probe itself and, therefore, only peripheral and scattered portions of the luminescence signal are collected. In addition, another disadvantage of this technique includes the failure to account for the lateral current in the p-n junction layers, which may lead to significant spreading of electroluminescence outside of the electrode area, resulting in a significant contribution measurement error. Further, this method suffers from the presence of measurement artifacts related to the contamination, high contact resistance, alignment difficulties, the present of particles and the like.
It is evident that the prior art includes a number of deficiencies. Therefore, it would be desirable to provide a method and system that cure these deficiencies of the prior art identified above.